Rubber composition

ABSTRACT

A rubber composition comprising a diene rubber, a reinforcing agent and a compound containing radicals capable of being stably present at room temperature in the presence of oxygen in the molecule thereof, selected from the group consisting of nitroxide radicals, hydrazyl radicals, allyloxyl radicals, and trityl radicals and the analogues thereof or a compound having at least one substituent group selected from amino groups, isocyanate groups, hydroxyl groups, carboxyl groups, oxirane groups, and thiirane groups.

TECHNICAL FIELD

The present invention relates to a rubber composition. More specificallyit relates to a rubber composition obtained by compounding a compoundcontaining free radicals having a powerful radical trapping characterinto a rubber composition, which is superior in processability, has ahigh gripping force and low heat buildup, prevents oxidative agingduring abrasion, improves the abrasion resistance, and is superior inthe balance of the high wet braking performance and low rollingresistance (i.e., tan δ balance).

BACKGROUND ART

Various attempts have been made to improve the processability of rubbercompositions, particularly rubber compositions for pneumatic tires, andthe other properties of tires and other products. There is particularlystrong need for a rubber composition superior in processability, high ingripping force of the tire, low in heat buildup, and improved inabrasion resistance. For example, Japanese Unexamined Patent Publication(Kokai) No. 62-148544 discloses a rubber composition containing areinforcing filler and isomaleimide compounded with a natural rubber orsynthetic diene rubber, to obtain the improved green strength and greenmodulus, a low heat buildup and excellent crack growth resistance.Further, Japanese Unexamined Patent Publication (Kokai) No. 7-304305discloses a pneumatic tire obtained from a composition comprised ofrubber in which a mixture of p-phenylene diamine antioxidant,2,2,4-trimethyl-1,2-dehydroquinoline (or its derivative) and a specificcarbon black is compounded, whereby, while maintaining an excellentsteering stability and high grip performance, the abrasion resistance isimproved. Further, there are needs for a rubber composition superior inprocessability, high in abrasion resistance when made a tire, andsuperior in the balance between the high wet braking performance and lowrolling resistance. The stabilization of a polymer with a stable freeradical is described in Japanese Unexamined Patent Publication (Kokai)No. 8-239510. The effect of preventing rubber deterioration with astable free radical has been proposed in Japanese Patent Application No.8-284080. On the other hand, the fact that a reaction of a rubber havinga reactive group such as an amino group with a carbon black reduces thehysteresis and decreases the rolling resistance is described in, forexample, Japanese Unexamined Patent Publication (Kokai) No. 8-269131.Further, Japanese Unexamined Patent Publication (Kokai) No. 8-283461,Japanese Unexamined Patent Publication (Kokai) No. 8-283462, etc.disclose rubber and carbon black are reacted using thiadiazole or ahydrazide compound, whereby the dispersibility is improved and the heatbuildup is reduced.

DISCLOSURE OF THE INVENTION

Accordingly, an object of the present invention is to provide a rubbercomposition having a superior processability, superior balance of highgrip/low heat buildup, and improved abrasion resistance.

Another object of the present invention is to provide a rubbercomposition having a superior processability, superior balance of highwet braking performance/low rolling resistance (i.e., tan δ balance),and improved abrasion resistance.

In accordance with the present invention, there is provided a rubbercomposition comprising 100 parts by weight of at least one diene rubberat least 40 parts by weight of at least one reinforcing agent and 0.1 to10 parts by weight of at least one compound containing, in the moleculethereof, a radical capable of being stably present at room temperaturein the presence of oxygen, selected from the group consisting ofnitroxide radicals, hydrazyl radicals, allyloxyl radicals, and tritylradicals and the analogues thereof.

In accordance with another aspect of the present invention, there isprovided a rubber composition comprising 100 parts by weight of at leastone diene rubber, at least 20 parts by weight of at least onereinforcing agent and 0.1 to 10 parts by weight of a compound containingat least one radical selected from the group consisting of nitroxideradicals, hydrazyl radicals, allyloxyl radicals, and trityl radicalshaving at least one substituent group selected from the group consistingof an amino group, isocyanate group, hydroxyl group, carboxyl group,oxirane group, and thiirane group and capable of being stably present atroom temperature in the presence of oxygen.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be explained below in the structure andfunctional effects thereof with reference to the drawings. FIG. 1(a),FIG. 1(b), FIG. 1(c), and FIG. 1(d) schematically illustrate thefunctions of preventing deterioration or aging in the rubber compositionaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The rubber compounded into the rubber composition of the presentinvention as the main component may be any diene rubber generally usedin various types of rubber compositions in the past, for example, dienerubbers such as natural rubbers (NR), polyisoprene rubbers (IR), variousstyrene-butadiene copolymer rubbers (SBR), various polybutadiene rubbers(BR), acrylonitrile-butadiene copolymer rubbers (NBR), butyl rubbers(IIR), alone or in any blend thereof.

As the reinforcing agent compounded into the rubber compositionaccording to the present invention, for example, carbon black, silica,etc. may be mentioned. In the first aspect, at least 40 parts by weight,preferably 50 to 120 parts by weight, are compounded into 100 parts byweight of the diene rubber. If the amount is too small, thereinforcement required for the rubber composition unpreferably cannot beobtained.

The carbon black capable of being used in the rubber composition of thepresent invention has a nitrogen specific surface area (N₂ SA) of,preferably, 20 to 200 m² /g, more preferably 50 to 170 m² /g, and a DBPoil absorption of, preferably, 60 to 130 ml/100 g, more preferably 80 to120 ml/100 g.

The silica capable of being used in the rubber composition of thepresent invention may include any silica (or white carbon) capable ofbeing used for rubber compositions and preferably has an N₂ SA of 80 to300 m² /g, more preferably 100 to 250 m² /g, and a DBP oil absorption of100 to 300 ml/100 g, more preferably 120 to 250 ml/100 g.

Note that the methods of measurement of the properties of the carbonblack and silica are as follows:

a) Nitrogen Specific Surface Area (N₂ SA)

According to method C of ASTM-D3037-78 "Standard Methods of TreatingCarbon Black-Surface Area by Nitrogen Adsorption".

b) DBP Oil Adsorption

Measured according to ASTM-D-3493.

According to the first aspect of the present invention, as an essentialcomponent, 0.1 to 10 parts by weight, preferably 0.5 to 5 parts byweight, of at least one compound containing, in the molecule thereof, aradical capable of being stably present at room temperature and in thepresence of oxygen and selected from the group consisting of nitroxideradicals, hydrazyl radicals, allyloxyl radicals, and trityl radicals andthe analogues thereof is compounded into 100 parts by weight of a dienerubber. If the amount is too small, the desired effect cannot beobtained, while if too large, the intended reinforcement necessary forthe rubber composition cannot be obtained, which is also not preferable.

As the compound containing in its molecule a radical stable at roomtemperature which can be used in the first aspect of the presentinvention, the following compounds may be illustrated: ##STR1##

where, in the above formulas (1) to (6), R 30 represents C₁ to C₃₀hydrocarbon which may contain O, N, S, P, F, Cl, Br, or I.

Specific examples are indicated below: ##STR2##

As explained above, according to the first aspect of the presentinvention, there is provided a rubber composition in which a compoundhaving a free radical having a powerful radical trapping character iscompounded. In the present invention, for example, the rubber adsorptioningredients formed on the carbon black are controlled to reduce theeffect of the rubber on the rubber matrix ingredient far from the carbonblack in the rubber composition as much as possible, whereby thephysical properties of the rubber can be improved. As the method forthis, it is possible to efficiently trap the radicals generated due tothe mechanochemical cleavage of the rubber chains with a shear forcegenerated during the mixing of the carbon black and the rubber with thecompound containing free radicals stably present at ordinary temperaturein the presence of oxygen to thereby prevent cross-linking of the rubberand reduce the excessive rubber adsorption ingredient. By this, it ispossible to reduce the rubber viscosity at the time when not vulcanizedand create a rubber having a good tan δ balance and obtain a rubberhaving a good processability and a good balance of the wet brakingperformance/low rolling resistance. Further, the compound having thenormally stable free radicals trap the radicals generated by themechanochemical cleavage of the rubber chains by the shear forcegenerated during abrasion so as to prevent cross-linking of the rubber,to suppress the generation of microdomains, to prevent a reduction inthe destructive physical properties, whereby the abrasion resistance isimproved.

As the reinforcing agent compounded into the second aspect of the rubbercomposition of the present invention, for example, carbon black andsilica may be mentioned. In this case, at least 20 parts by weight,preferably 40 to 60 parts by weight, are compounded into 100 parts byweight of the diene rubber. If the amount is too small, thereinforcement required for the rubber composition unpreferably cannot beobtained.

According to the second aspect of the present invention, as theessential component, 0.1 to 10 parts by weight, preferably 0.5 to 5parts by weight, of a compound having at least one radical selected fromthe group consisting of a nitroxide radical, hydrazyl radical, allyloxylradical, and trityl radical having at least one substituent groupselected from the group consisting of an amino group, isocyanate group,hydroxyl group, carboxyl group, oxirane group, and thiirane group andcapable of being stably present at room temperature and in the presenceof oxygen is compounded into 100 parts by weight of a diene rubber. Ifthe amount is too small, the desired effect cannot be obtained, whileconversely if too large, the reinforcement required for the rubbercomposition unpreferably cannot be obtained.

As the compound which may be used in the second aspect of the presentinvention, the following compounds may be illustrated:

Substituted Nitroxide Radical (Piperidinyloxy) (see Formula (I))##STR3##

wherein, in formula (I), R is at least one of C, 0, N, S, P, a C₁ to C₃₀alkylene group, and a C₆ to C₃₀ aryl group or a single bond, R¹ to R⁴are, independently, hydrogen, or C₁ to C₄ alkyl group such as methylgroup, ethyl group, A is independently an amino group, isocyanate group,hydroxyl group, carboxyl group, oxirane group, or thiirane group, and nis an integer of 1 to 6.

Representative examples of the compound having substituted nitroxideradicals shown in formula (I) and the other compounds containingsubstituted nitroxide radicals are as follows: ##STR4##

wherein, R, R¹ to R⁴, A, and n are as defined above.

Representative examples of compounds containing substituted nitroxideradicals shown in formula (II) or (III) are as follows: ##STR5##

As the other examples of the nitroxide radicals, the followingsubstituents of the radical compounds can also be mentioned as compoundscontaining nitroxide radicals of the present invention: ##STR6##

Giving examples of substituted hydrazyl radical compounds, the followingsubstituents of the compounds may be mentioned. ##STR7##

Giving examples of substituted allyloxy radical compounds, the followingsubstituents of the compounds may be mentioned. ##STR8##

Giving examples of substituted trityl radical compounds and theiranalogues, the following substituents of the compounds may be mentioned.##STR9##

According to the second aspect of the present invention, as explainedabove, by using a stable free radical compound having specificsubstituent groups, it is possible to obtain a rubber composition havingsuperior abrasion resistance and superior tan δ balance (0° C./60° C.)(that is, high wet braking performance/low rolling resistance balance).A schematic explanation of this taking as an example 4-amino-TEMPOfollows:

As shown in FIG. 1, when the cross-linked structure rubber molecule (seeFIG. 1(a)) is optically, thermally, or mechanically cleavage andradicals are generated (see FIG. 1(b)), the radicals are immediatelytrapped by the 4-amino-TEMPO as shown in FIG. 1(c), and therefore, it ispossible to effectively prevent the deterioration or aging or otherphenomena of the rubber due to the generation of free radicals in therubber molecule. However, as a result of this trapping of radicals, thenumber of the terminals of the rubber increase and, as a result, thephysical properties of the rubber make worse. Therefore, in the presentinvention, by introducing an amino group, an isocyanate group, ahydroxyl group, a carboxyl group, etc. which are reactive with thehydroxy group or carbonyl group on the surface of the carbon black orsilica into the free radical (nitroxide) compound, as shown in FIG.1(d), the terminals of the trapped rubber react with the surface of thecarbon black (or silica), prevent an increase of the number ofterminals, and produce a strong carbon gel (or gel with silica), wherebythe physical properties of the rubber are improved. In particular, it ispossible to improve the abrasion resistance and remarkably improve thehigh wet braking performance/low rolling resistance balance.

The rubber composition according to the present invention may contain,in addition to the above-mentioned essential components, a vulcanizationor cross-linking accelerator, various types of oil, an antioxidant,plasticizer, and other various additives generally compounded for tiresor for other general rubber use. The blend may be mixed and vulcanizedto form a composition by a general method and used for vulcanization orcross-linking. As long as the amounts of these additives do notcontravene the object of the present invention, it is possible to usethe conventional general amounts of formulation.

EXAMPLES

The present invention will be explained below in further detail usingExamples, Standard Examples, and Comparative Examples, but the scope ofthe present invention is, of course, not limited to these Examples.

Standard Example I-1, Examples I-1 to I-4, and Comparative Examples I-1to I-2

Preparation of Samples

The ingredients other than the vulcanization accelerator and sulfur inthe formulations shown in Table I-1 were mixed in a 1.8 liter closedtype mixer for 3 to 5 minutes. When the temperature of the mixturereaches 165±5° C., the mixtures were discharged. The vulcanizationaccelerator and sulfur were then mixed by an 8-inch open roll with themasterbatch obtained above to obtain a rubber composition. Theunvulcanized physical properties of the rubber compositions thusobtained were measured.

Next, the composition was vulcanized by pressing the composition in15×15×0.2 cm mold at 160° C. for 20 minutes to prepare the desired testpiece (i.e., rubber sheet) which was then evaluated for vulcanizedphysical properties.

                  TABLE I-1                                                       ______________________________________                                               Stand.                        Comp. Comp.                                     Ex.   Ex.    Ex.    Ex.  Ex.  Ex.   Ex.                                       I-1   I-1    I-2    I-3  I-4  I-1   I-2                                ______________________________________                                        [Composition                                                                  (parts by                                                                     weight)]                                                                      Natural  100.0   100.0  100.0                                                                              100.0                                                                              100.0                                                                              100.0 100.0                            rubber (NR)*.sup.1                                                            Carbon   50.0    50.0   50.0 50.0 50.0 50.0  50.0                             black*.sup.2                                                                  TEMPO*.sup.3                                                                           --      1.0    3.0  --   --   --    --                               DPPH*.sup.4                                                                            --      --     --   3.0  --   --    --                               Triphenyl-                                                                             --      --     --   --   3.0  --    --                               phenoxyl*.sup.5                                                               Zinc White #3                                                                          3.0     3.0    3.0  3.0  3.0  3.0   3.0                              Industrial                                                                             1.0     1.0    1.0  1.0  1.0  1.0   1.0                              stearic acid                                                                  Antioxidant                                                                            1.0     1.0    1.0  1.0  1.0  1.0   5.0                              6C*.sup.6                                                                     Aromatic --      --     --   --   --   5.0   --                               process oil                                                                   Oil treated                                                                            1.1     1.1    1.1  1.1  1.1  1.1   1.1                              powdered                                                                      sulfur                                                                        Vulcanization                                                                          1.1     1.1    1.1  1.1  1.1  1.1   1.1                              accelerator                                                                   NS*.sup.7                                                                     [Unvulcanized                                                                 physical                                                                      properties]                                                                   Mooney   70      61     57   58   62   63    67                               viscosity                                                                     [Vulcanized                                                                   physical                                                                      properties]                                                                   tanδ (0° C.)                                                              0.239   0.235  0.238                                                                              0.237                                                                              0.235                                                                              0.235 0.235                            tanδ (60° C.)                                                             0.103   0.100  0.094                                                                              0.091                                                                              0.101                                                                              0.115 0.110                            Abrasion 100     111    121  117  110  85    102                              resistance                                                                    (index)                                                                       ______________________________________                                         *.sup.1 : SIR20 (natural rubber)                                              *.sup.2 : N220 (made by Showa Cabot, carbon black, N.sub.2 SA = 112           m.sup.2 /g, DBP oil adsorption = 112 ml/100 g)                                *.sup.3 : 2,2,6,6tetramethylpiperidinyloxy (made by Aldrich Chemical Col.     Inc.)                                                                         *.sup.4 : 2,2diphenyl-1-picrylhydrazyl (made by Aldrich Chemical Co. Inc.     *.sup.5 : Made by Aldrich Chemical Co. Inc.                                   *.sup.6 : Made by Sumitomo Chemical,                                          Nphenyl-N(1,3-dimethylbutyl)-p-phenylenediamine                               *.sup.7 : Made by Ouchi Shinko Chemical Industrial,                           Ntert-butyl-2-benzothiazole-sulfenamide                                  

The test methods of the unvulcanized physical properties and thevulcanized physical properties of the compositions obtained in theExamples were as follows:

Unvulcanized Physical Properties

1) Mooney viscosity

Measured according to JIS (Japan Industrial Standard) K 6300 at 100° C.

Vulcanized Physical Properties

1) tan δ

A viscoelasticity spectrometer (made by Toyo Seiki) was used to measuretan δ at temperatures of 0° C. and 60° C., an initial strain of 10%, adynamic strain of +2%, and a frequency of 20 Hz. The tan δ at 0° C. isthe measure of the gripping force on wet roads and the tan δ at 60° C.is on dry roads. In both cases, the larger the tan δ, the greater thegripping force of the tire. Further, the tan δ at 60° C. converselyshows the braking resistance. In this case, the smaller the value, thesmaller the braking resistance.

2) Abrasion Resistance

A Lambourn abrasion tester (made by Iwamoto Seisakusho) was used tomeasure the abrasion loss at a temperature of 20° C. The wear loss wasindicated as an index.

Abrasion resistance (index)=[(loss of Standard Example)/(loss ofsample)]×100

(Note) The larger the index, the better the abrasion resistance.

Standard Example I-2, Examples I-5 to I-8, and Comparative Examples I-3to I-4

The same procedure was follows as in the previous Examples to preparerubber compositions of formulations shown in Table I-2 which were thenevaluated in physical properties. The results are shown in Table I-2.

                  TABLE I-2                                                       ______________________________________                                               Stand.                        Comp. Comp.                                     Ex.   Ex.    Ex.    Ex.  Ex.  Ex.   Ex.                                       I-2   I-5    I-6    I-7  I-8  I-3   I-4                                ______________________________________                                        [Composition                                                                  (parts by                                                                     weight)]                                                                      Polyisoprene                                                                           100.0   100.0  100.0                                                                              100.0                                                                              100.0                                                                              100.0 100.0                            rubber (IR)*.sup.1                                                            Carbon   50.0    50.0   50.0 50.0 50.0 50.0  50.0                             black*.sup.2                                                                  TEMPO*.sup.2                                                                           --      1.0    3.0  --   --   --    --                               DPPH*.sup.2                                                                            --      --     --   1.0  3.0  --    --                               Triphenyl-                                                                             --      --     --   --   --   3.0   --                               phenoxyl*.sup.2                                                               Zinc White #3                                                                          3.0     3.0    3.0  3.0  3.0  3.0   3.0                              Industrial                                                                             1.0     1.0    1.0  1.0  1.0  1.0   1.0                              stearic acid                                                                  Antioxidant                                                                            1.0     1.0    1.0  1.0  1.0  1.0   5.0                              6C*.sup.2                                                                     Aromatic --      --     --   --   --   5.0   --                               process oil                                                                   Oil treated                                                                            1.1     1.1    1.1  1.1  1.1  1.1   1.1                              powdered                                                                      sulfur                                                                        Vulcanization                                                                          1.1     1.1    1.1  1.1  1.1  1.1   1.1                              accelerator                                                                   NS*.sup.2                                                                     [Unvulcanized                                                                 physical                                                                      properties]                                                                   Mooney   70      61     57   58   62   63    67                               viscosity                                                                     [Vulcanized                                                                   physical                                                                      properties]                                                                   tanδ (0° C.)                                                              0.319   0.335  0.337                                                                              0.330                                                                              0.328                                                                              0.235 0.235                            tanδ (60° C.)                                                             0.190   0.182  0.179                                                                              0.180                                                                              0.187                                                                              0.115 0.110                            Abrasion 100     115    120  118  112  81    104                              resistance                                                                    (index)                                                                       ______________________________________                                         *.sup.1 : Nipol IR2200 (made by Nihon Zeon, IR)                               *.sup.2 : See notes of Table I1.                                         

Standard Examples I-3 to I-4, Examples I-9 to I-11, and ComparativeExamples I-5 to I-6

The same procedure was follows as in the previous Examples to preparerubber compositions of formulations shown in Table I-3 which were thenevaluated in physical properties. The results are shown in Table I-3.

                  TABLE I-3                                                       ______________________________________                                        Stand.             Comp.   Stand.          Comp.                              Ex.         Ex.    Ex.     Ex.   Ex.  Ex.  Ex.                                I-3         I-9    I-5     I-4   I-10 I-11 I-6                                ______________________________________                                        [Com-                                                                         position                                                                      (parts by                                                                     weight)]                                                                      SBR*.sup.1                                                                            100.0   100.0  100.0 --    --   --   --                               SBR*.sup.2                                                                            --      --     --    150.0 150.0                                                                              150.0                                                                              150.0                            Carbon  50.0    50.0   50.0  --    --   --   --                               black*.sup.3                                                                  Carbon  --      --     --    95.0  95.0 95.0 95.0                             black*.sup.4                                                                  TEMPO*.sup.5                                                                          --      3.0    --    --    3.0  --   --                               DPPH*.sup.5                                                                           --      --     --    --    --   3.0  --                               Zinc White                                                                            3.0     3.0    3.0   3.0   3.0  3.0  3.0                              #3                                                                            Industrial                                                                            1.0     1.0    1.0   1.0   1.0  1.0  1.0                              stearic acid                                                                  Antioxidant                                                                           1.0     1.0    5.0   1.0   1.0  1.0  1.0                              6C*.sup.5                                                                     Aromatic                                                                              --      --     --    --    --   --   --                               process oil                                                                   Oil treated                                                                           2.4     2.4    2.4   2.4   2.4  2.4  2.4                              powdered                                                                      sulfur                                                                        Vul-    1.6     1.6    1.6   1.6   1.6  1.6  1.6                              canization                                                                    accelerator                                                                   CZ*.sup.6                                                                     Vul-    0.1     0.1    0.1   0.1   0.1  0.1  0.1                              canization                                                                    accelerator                                                                   DPG*.sup.7                                                                    [Un-                                                                          vulcanized                                                                    physical                                                                      properties]                                                                   Mooney  61      49     55    76    68   69   74                               viscosity                                                                     [Vulcanized                                                                   physical                                                                      properties]                                                                   tanδ (0° C.)                                                             0.291   0.293  0.299 0.872 0.891                                                                              0.897                                                                              0.883                            tanδ (60° C.)                                                            0.138   0.130  0.144 0.401 0.387                                                                              0.380                                                                              0.412                            Abrasion                                                                              100     113    105   100   110  112  105                              resistance                                                                    (index)                                                                       ______________________________________                                         *.sup.1 : Nipol 1502 (made by Nihon Zeon SBR)                                 *.sup.2 : Nipol 9528 (made by Nihon SBR, 33.3% oil extended)                  *.sup.3 : N339 (made by Tokai Carbon, carbon black, N.sub.2 SA = 92           m.sup.2 /g, DBP oil adsorption = 117 ml/100 g)                                *.sup.4 : N114 (made by Tokai Carbon, carbon black, N.sub.2 SA = 153          m.sup.2 /g, DBP oil adsorption = 127 ml/100 g)                                *.sup.5 : See notes of Table I1.                                              *.sup.6 : Made by Ouchi Shinko Chemical Industrial,                           Ncyclohexyl-2-benzothiazyl sulfenamide                                        *.sup.7 : Made by Ouchi Shinko Chemical Industrial, diphenyl guanidine   

Examples II-1 to II-6, Reference Examples II-1 to II-2, and ComparativeExamples II-1 to II-2

The ingredients other than the vulcanization accelerator and sulfur inthe formulations shown in Table II-1 were mixed in a 1.8 liter closedtype mixer for 3 to 5 minutes. When reaching 165±5° C., the mixture wasdischarged. The vulcanization accelerator and sulfur were mixed by an8-inch open roll with the masterbatch to obtain a rubber composition.The unvulcanized physical property (Mooney viscosity) of the rubbercomposition obtained was measured.

Next, the composition was vulcanized by pressing in 15×15×0.2 cm mold at160° C. for 20 minutes to prepare the desired test piece (rubber sheet)which was then evaluated for vulcanized physical properties. The resultsare shown in Table II-1.

                  TABLE II-1                                                      ______________________________________                                                     Comp.   Ref.                                                                  Ex. II-1                                                                              Ex. II-1  Ex. II-1                                                                            Ex. II-2                                 ______________________________________                                        [Composition (parts                                                           by weight)]                                                                   Polyisoprene rubber                                                                        100.0   100.0     100.0 100.0                                    (IR)                                                                          Styrene butadiene                                                                          --      --        --    --                                       rubber (SBR)                                                                  Carbon black 50      50        50    50                                       TEMPO        --      1         --    --                                       NHTEMPO      --      --        1     --                                       NCOTEMPO     --      --        --    1                                        Zinc White #3                                                                              5       5         5     5                                        Industrial stearic                                                                         1       1         1     1                                        acid                                                                          Antioxidant 6C                                                                             3       3         3     3                                        Oil treated powdered                                                                       1.1     1.1       1.1   1.1                                      sulfur                                                                        Vulcanization                                                                              1.1     1.1       1.1   1.1                                      accelerator NS                                                                [Unvulcanized                                                                 physical properties]                                                          Mooney viscosity                                                                           80      68        75    70                                       [Vulcanized physical                                                          properties]                                                                   tanδ (0° C.)                                                                  0.305   0.305     0.301 0.298                                    tanδ (60° C.)                                                                 0.188   0.186     0.162 0.168                                    tanδ balance                                                                         1.62    1.64      1.86  1.77                                     (0° C./60° C.)                                                  Abrasion resistance                                                                        100     104       104   107                                      (index)                                                                       ______________________________________                                                 Comp.                                                                         Ex.     Ref.                                                                  II-2    Ex. II-2                                                                              Ex. II-3                                                                            Ex. II-4                                                                            Ex. II-5                                                                            Ex. II-6                           ______________________________________                                        [Composition                                                                  (parts by                                                                     weight)]                                                                      Polyisoprene                                                                           --      --      --    --    --    --                                 rubber (IR)                                                                   Styrene  100     100     100   100   100   100                                butadiene                                                                     rubber (SBR)                                                                  Carbon black                                                                           50      50      50    50    50    50                                 TEMPO    --      1       --    --    --    --                                 NHTEMPO  --      --      1     --    --    --                                 NCOTEMPO --      --      --    1     --    --                                 MDP-TEMPO                                                                              --      --      --    --    1     --                                 P-TEMPO  --      --      --    --    --    1                                  Zinc White #3                                                                          5       5       5     5     5     5                                  Industrial                                                                             1       1       1     1     1     1                                  stearic acid                                                                  Antioxidant                                                                            3       3       3     3     3     3                                  6C                                                                            Oil treated                                                                            1.1     1.1     1.1   1.1   1.1   1.1                                powdered                                                                      sulfur                                                                        Vulcanization                                                                          1.1     1.1     1.1   1.1   1.1   1.1                                accelerator                                                                   NS                                                                            [Unvulcanized                                                                 physical                                                                      properties]                                                                   Mooney   84      80      100   92    113.0 74.2                               viscosity                                                                     [Vulcanized                                                                   physical                                                                      properties]                                                                   tanδ (0° C.)                                                              0.307   0.308   0.298 0.302 0.305 0.309                              tanδ (60° C.)                                                             0.226   0.225   0.212 0.218 0.218 0.218                              tanδ balance                                                                     1.36    1.37    1.41  1.39  1.4   1.42                               (0° C./60° C.)                                                  Abrasion 100     103     105   106   105   104                                resistance                                                                    (index)                                                                       ______________________________________                                         IR: Nipol IR2200 (made by Nihon Zeon)                                         SBR: Nipol 1502 (made by Nihon Zeon)                                          Carbon black: Dia Black 1 (made by Mitsubishi Chemical)                       TEMPO: 2,2,6,6tetramethylpiperidinyloxy (made by Aldrich Chemical Co.         Inc.)                                                                         NHTEMPO: 4amino-2,2,6,6-tetramethylpiperidinyloxy (made by Aldrich            Chemical Co. Inc.)                                                            NCOTEMPO: 4isocyanate-2,2,6,6-tetramethylpiperidinyloxy                       6C: Nphenyl-N(1,3-dimethylbutyl)-p-phenylenediamine (made by Sumitomo         Chemical)                                                                     NS: Ntert-butyl-2-benzothiazylsulfenamide (made by Ouchi Shinko Chemical      Industrial)                                                                   ##STR10##     6C: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (made by Sumitomo     Chemical)

NS: N-tert-butyl-2-benzothiazylsulfenamide (made by Ouchi ShinkoChemical Industrial)

The test methods of the unvulcanized physical properties and thevulcanized physical properties of the compositions obtained in theExamples were as mentioned above.

INDUSTRIAL APPLICABILITY

As explained above, according to the present invention, by compounding aspecific compound containing free radicals having a powerful radicaltrapping function into a rubber composition, it is possible to obtain arubber composition where the free radicals of the rubber generatedduring the mixing are trapped, where the cleavage of the chains of therubber and the generation of carbon gel can be suppressed, which issuperior in processability, which is superior in balance of highgrip/low heat buildup, and which is improved in abrasion resistance.Further, according to another aspect of the present invention, byintroducing an amino group, isocyanate group, hydroxyl group, carboxylgroup, oxirane group, or thiirane group into the specific compoundcontaining free radicals having a powerful radical trapping function, asa substituent, and compounding the same into the rubber composition, itis possible to obtain a rubber composition which is superior in balanceof high wet performance/low rolling resistance and which is improved inabrasion resistance.

We claim:
 1. A rubber composition consisting essentially of (i) 100parts by weight of at least one diene rubber, (ii) at least 40 parts byweight of at least one reinforcing agent and (iii) 0.1 to 10 parts byweight of at least one compound containing, in the molecule thereof, aradical capable of being stably present at room temperature in thepresence of oxygen, selected from the group consisting of nitroxideradicals, hydrazyl radicals, allyloxyl radicals, and trityl radicals andthe analogues thereof, and (iv) additives generally compounded forgeneral rubber use.
 2. A rubber composition as claimed in claim 1,wherein the compound containing radicals capable of being stably presentat room temperature and in the presence of oxygen aretetramethylpiperidinyloxy and the analogues thereof.
 3. A rubbercomposition as claimed in claim 1, wherein the compound containingradicals capable of being stably present at room temperature in thepresence of oxygen are 2,2-diphenyl-1-picrylhydrazyl and the analoguesthereof.
 4. A rubber composition as claimed in any one of claims 1 to 3,wherein the reinforcing agent is a carbon black having a nitrogenspecific surface area (N₂ SA) of 20 to 200 m² /g and a DBP oilabsorption of 60 to 130 ml/100 g.
 5. A rubber composition as claimed inany one of claims 1 to 3, wherein the reinforcing agent is a silicahaving a nitrogen specific surface area or N₂ SA of 80 to 300 m² /g anda DBP oil absorption of 100 to 300 ml/100 g.
 6. A pneumatic tireobtained using a rubber composition according to any one of claims 1 to3.
 7. A rubber composition as claimed in claim 1, wherein the amount ofthe reinforcing agent is at least 20 parts by weight based upon 100parts by weight of the diene starting rubber and the compoundcontaining, in the molecule thereof, a radical capable of being stablypresent at room temperature in the presence of oxygen has at least onesubstituent group selected from the group consisting of an amino group,isocyanate group, hydroxyl group, carboxyl group, oxirane group, andthiirane group.
 8. A rubber composition as claimed in claim 7, whereinthe compound containing radicals capable of being stably present at roomtemperature in the presence of oxygen is tetramethylpiperidinyloxy andits analogues.
 9. A pneumatic tire obtained using a rubber compositionaccording to claim 7 or
 8. 10. A rubber composition according to claim4, wherein the reinforcing agent is a silica having a nitrogen specificsurface area or N₂ SA of 80 to 300 m² /g and a DBP oil absorption of 100to 300 ml/100 g.
 11. A pneumatic tire obtained using a rubbercomposition according to claim
 4. 12. A pneumatic tire obtained using arubber composition according to claim
 5. 13. A pneumatic tire obtainedusing a rubber composition according to claim
 10. 14. A method fortrapping radicals generated in diene rubber during the mixing of arubber composition with a radical capable of being stably present atroom temperature in the presence of oxygen, selected from the groupconsisting of nitroxide radicals, hydrazyl radicals, allyloxyl radicals,and trityl radicals and the analogues thereof, said compositioncontaining 100 parts by weight of at least one diene rubber, at least 40parts by weight of at least one reinforcing agent and 0.1 to 10 parts byweight of at least one compound containing, in the molecule thereof,said radical.
 15. A rubber composition comprising (i) 100 parts byweight of at least one diene rubber, (ii) at least 40 parts by weight ofat least one reinforcing agent and (iii) 0.1 to 10 parts by weight of atleast one compound containing, in the molecule thereof, a radicalcapable of being stably present at room temperature in the presence ofoxygen, selected from the group consisting of nitroxide radicals,hydrazyl radicals, allyloxyl radicals, and trityl radicals and theanalogues thereof, wherein the compound containing radicals capable ofbeing stably present at room temperature and in the presence of oxygenis selected from the group consisting of tetramethylpiperidinyloxy andthe analogues thereof.
 16. A rubber composition according to claim 15,wherein the reinforcing agent is a carbon black having a nitrogenspecific surface area or N₂ SA of 20 to 200 m² /g and a DBP oilabsorption of 60 to 130 ml/100 g.